create table rate_between_responses (
  base text references currencies not null,
  target text references currencies not null,
  rate numeric not null,
  timestamp bigint not null
);
comment on table rate_between_responses is '
  flowerate response for exchange rate between two currencies
';

comment on column rate_between_responses.base is '
  base currency
';
comment on column rate_between_responses.target is '
  targey currency
';
comment on column rate_between_responses.rate is '
  exchange rate, target currency to base currency
';
comment on column rate_between_responses.timestamp is '
  epoch timestamp of returned exchange rate
';